In a large skillet, heat the vegetable oil over medium-high heat. Add the lamb pieces and sear until browned on all sides. Remove from the skillet and set aside.
In the same skillet, add the chopped onion, garlic, and ginger. Sauté until the onion is translucent, about 5 minutes.
Stir in the curry powder, cumin, coriander, and turmeric. Cook for another 1-2 minutes until the spices are fragrant.
Transfer the sautéed onion and spice mixture to the slow cooker. Add the seared lamb, coconut milk, vegetable broth, and diced tomatoes. Stir to combine.
Add the sliced carrots and diced bell pepper to the slow cooker. Season with salt and pepper.
Cover and cook on low for 8 hours or on high for 4 hours, until the lamb is tender.
In the last 30 minutes of cooking, stir in the frozen peas and adjust the seasoning if necessary.
Once done, garnish with fresh cilantro before serving.
Notes
Serve the curry over a bed of fluffy basmati rice, and garnish with additional cilantro and a sprinkle of chili flakes for a pop of color.